1. Field of the Invention
The present invention relates to a magnetic head for perpendicular recording and a magnetic disk apparatus equipped with the magnetic head for perpendicular recording.
2. Description of the Related Art
To increase a recording capacity per unit area of a magnetic disk, the bit length and the track width must be reduced to decrease the size of one bit cell as a minimum unit of recording information. In the current longitudinal recording system, however, there arises the problem that bit cell reduction loses a written signal due to the influence of thermal fluctuation. To solve this problem, a perpendicular recording system magnetizes a medium in the perpendicular direction to write signal information.
The recording head of a magnetic disk apparatus writes signal information onto a medium. In the perpendicular recording system, there are a system which uses a double-layered perpendicular medium having a soft magnetic underlayer and a system which uses a single-layer perpendicular medium not having an underlayer. A structure which combines a double-layered perpendicular medium with a single-pole head having a main pole and an auxiliary pole can apply a more intense magnetic field to a medium.
When the cross-sectional area of a main pole of a single-pole head is flux enhanced to the front end thereof, magnetic flux in the magnetic pole is concentrated on the front end of the main pole so that a locally intense magnetic field can be applied to a medium. When a pole tip having a high permeability is arranged on the front end of the main pole, the flow of magnetic flux at the front end of the main pole can be smooth. Further, the processing dimension accuracy at the front end of the main pole can be enhanced.
The example described in Japanese Published Unexamined Patent Application No. Hei 11-275188 discloses that when a main pole has a pole tip, arrangement of a pole tip and a main pole having the pole tip and arrangement of a pole tip and an auxiliary pole are defined so that the magnetic field gradient of a perpendicular magnetic field component on the trailing side can be improved. This prevents the influence of a magnetic field from the surface of the main pole having the pole tip opposite to a medium, but does not consider increase of the leakage magnetic flux by flux enhancing in the main pole and the pole tip.
In the above prior art, the leakage magnetic field is locally increased due to the influence of abrupt flux enhancing in the flux enhanced part in the main pole and the pole tip and particularly, the flux enhanced end in which the cross-sectional area of the main pole is smallest in the flux enhanced part, resulting in deterioration of the magnetic field gradient in a profile of a perpendicular magnetic field. In addition, the leakage magnetic field from the front or side surface of the main pole or the pole tip will also reduce the magnetic field gradient. An object of the present invention is to improve a magnetic field gradient in a distribution of a perpendicular magnetic field which writes the boundary of a bit cell, that is, a magnetic field gradient on the trailing side of a profile of a perpendicular magnetic field in the down track direction and a magnetic field gradient near both ends of a track of a profile of a perpendicular magnetic field in the cross track direction and to realize a high areal recording density by considering arrangement of the flux enhanced part or the flux enhanced end of a main pole or a pole tip and the front or side surface of the main pole or the pole tip.
In the present invention, part or all of the flux enhanced part or the flux enhanced end of a main pole or a pole tip is arranged on the leading side rather than a vertical plane including the trailing edge of the air bearing surface of the main pole so as to improve a magnetic field gradient of a profile of a perpendicular magnetic field on the trailing side and near both ends of a track width. In addition, the front or side surface of the main pole or the pole tip is arranged to the center of the main pole so as to improve a magnetic field gradient of the profile of a perpendicular magnetic field on the trailing side and near both ends of the track width.